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Designing highly efficient purely organic phosphors at room temperature remains a challenge because of fast non-radiative processes and slow intersystem crossing (ISC) rates. The majority of them emit only single component phosphorescence. Herein, we have prepared 3 isomers (o, m, p-bromophenyl)-bis(2,6-dimethylphenyl)boranes. Among the 3 isomers (o-, m- and p-BrTAB) synthesized, the ortho-one is the only one which shows dual phosphorescence, with a short lifetime of 0.8 ms and a long lifetime of 234 ms in the crystalline state at room temperature. Based on theoretical calculations and crystal structure analysis of o-BrTAB, the short lifetime component is ascribed to the T 1 M state of the monomer which emits the higher energy phosphorescence. The long-lived, lower energy phosphorescence emission is attributed to the T 1 A state of an aggregate, with multiple intermolecular interactions existing in crystalline o-BrTAB inhibiting nonradiative decay and stabilizing the triplet states efficiently., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The synthesis and characterization of 10-(dimesitylboryl)-N,N-di-p-tolylbenzo[c]phenanthren-4-amine (3-B(Mes) 2 -[4]helix-9-N(p-Tol) 2 1) and 13-(dimesitylboryl)-N,N-di-p-tolyldibenzo[c,g]phenanthren-8-amine (3-B(Mes) 2 -[5]helix-12-N(p-Tol) 2 2) are reported herein. Their electrochemical and photophysical properties have been studied experimentally and theoretically. The donor and acceptor-substituted helicene derivatives exhibit moderate fluorescence quantum yields in THF (Φ f =0.48 and 0.61 for 1 and 2, respectively), which are higher than unsubstituted ones (Φ f =0.18 for [4]helicene; Φ f <0.05 for [n]helicenes (n≥5)). In the solid state, the Φ f values are higher (Φ f =1.00 and 0.55 for 1 and 2, respectively) than those in solution, most likely due to the restrictions of molecular motions. The S 1 ←S 0 transitions of 1 and 2 are predominately HOMO→LUMO transitions. Upon excitation with UV light, the interplanar angle between the two terminal aryl rings of the [5]helix core of 2 decreases (S 1 state compared with S 0 state), which is similar to placing a spring under an external force., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)